selling existing theme under gpl 2.0 license after customizations

Hello I’m new on Envato. I’ve modified the “Storefront Theme” created by WooThemes under the gpl 2.0 license, to create my own theme. I want to sell my custom theme, Storefront based, on Themeforest but I don’t know if it is possible because of WooThemes property. GPL 2.0 license allows to sell it, respecting the licensing terms, but Themeforest?

Thanks in advance

You’d need to check with WooThenes but I seem to remember this is not allowed